Plasma cell clone immunophenotypic characteristics in patients with systemic AL-amyloidosis

   Immunophenotypic features of plasma cells (pC) in patients with systemic AL‑amyloidosis (AL‑A) are not fully characterized. The bone marrow of 113 patients with first diagnosed systemic AL‑A was studied by 10‑color flow cytofluorimetry. Three densities of differentiation antigen expression were distinguished: negative – less than 10 % of aberrant cells expressed antigen, partial – 10–90 % of cells expressed antigen, positive – more than 90 % of cells expressed antigen. Patients were divided into three groups. Group 1 included 76 patients with AL‑A and a PC count of less than 10 %. The second group consisted of 25 patients with a PC count greater than 10 % but without evidences of symptomatic multiple myeloma. The third group included 12 patients with a PC count greater than 10 % and symptomatic CRAb (AL‑A combined with multiple myeloma). 75 patients received first‑line therapy, including bortezomib, cyclophosphamide, and dexamethasone. When comparing the immunophenotype of aberrant PCs of each individual patient by means of a heat map, no complete match was found in any case, which confirms the uniqueness of clonal PC biology and their high heterogeneity. It was found that aberrant PCs lost expression of CD19 in 95.6 % of cases, CD45 in 78.6 % of patients, CD81 in 37.5 %, and CD27 in 36 %. CD20 was expressed in 7.7 % of patients, CD56 in 48.2 %, and CD117 in 36.8 %. A positive but low (dim) density of CD38 expression was detected in 45 % of patients. There were no statistically significant differences in the expression profile of CD19, CD20, CD27, CD38, CD45, CD56, CD117, CD138, CD200, and CD319 between the patient groups. The frequency of CD269 (bCMA) expression on pC varied depending on the size of the morphologic substrate. Partial expression of Cd269 (bCMA) was detected in 46.7 % of patients in group 1; 84.7 % in group 2 and 100 % in group 3 (p = 0.02). No positive, including high, Cd269 expression, was detected in any AL‑A patient in all three groups. A negative correlation of CD27 expression with the depth of hematologic response on therapy with bortezomib was established: in the absence of CD27 expression, a deep hematologic response was achieved in 87.5 % of cases, and with positive expression of this marker in only 35 % of patients (p = 0.02).

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